Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table. CMP polishing pads often comprise two or more layers, for example a polishing layer and a bottom (e.g., subpad) layer, which are joined together through the use of an adhesive, such as a hot-melt adhesive or a pressure-sensitive adhesive. Such a multi-layer polishing pad is disclosed, for example, in U.S. Pat. No. 5,257,478.
In polishing the surface of a workpiece, it is often advantageous to monitor the polishing process in situ. One method of monitoring the polishing process in situ involves the use of a polishing pad having a “window” that provides a portal through which light can  pass to allow the inspection of the workpiece surface during the polishing process. Such polishing pads having windows are known in the art and have been used to polish workpieces, such as semiconductor devices. For example, U.S. Pat. No. 5,893,796 discloses removing a portion of a polishing pad to provide an aperture and placing a transparent polyurethane or quartz plug in the aperture to provide a transparent window. Similarly, U.S. Pat. No. 5,605,760 provides a polishing pad having a transparent window formed from a solid, uniform polymer material that is cast as a rod or plug. The transparent plug or window typically is integrally bonded to the polishing pad during formation of the polishing pad (e.g., during molding of the pad) or is affixed in the aperture of the polishing pad through the use of an adhesive.
Prior art polishing pads that rely on adhesives to join together polishing pad layers or to affix windows within the polishing pad have many disadvantages. For example, the adhesives often have harsh fumes associated with them and typically require curing over 24 hours or more. Moreover, the adhesive can be susceptible to chemical attack from the components of the polishing composition, and so the type of adhesive used in joining pad layers or attaching a window to the pad has to be selected on the basis of what type of polishing system will be used. Furthermore, the bonding of the pad layers or windows to the polishing pad is sometimes imperfect or degrades over time. This can result in delamination and buckling of the pad layers and/or leakage of the polishing composition between the pad and the window. In some instances, the window can become dislodged from the polishing pad over time. Methods for forming integrally molded polishing pad windows can be successful in avoiding at least some of these problems, but such methods are often costly and are limited in the type of pad materials that can be used and the type of pad construction that can be produced.
Thus, there remains a need for effective multi-layer polishing pads and polishing pads comprising translucent regions (e.g., windows) that can be produced using efficient and inexpensive methods without relying on the use of an adhesive. The invention provides such polishing pads, as well as methods of their use. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.